1. Field of the Invention
The present invention generally relates to a wall mounted motion detection system and, more particularly, is concerned with a combination lens and window housing assembly for a motion detection system and a combination lens and window retainer employed therein for supporting both an optical lens and an optical window in a desired arrangement.
2. Description of the Prior Art
A passive infrared motion detection system detects heat energy radiated or emitted by an object, such as a body of a person, moving across a field of view of a heat sensor, such as a pyroelectric detector, of the motion detection system. The motion detection system must be capable of distinguishing between background temperature and a temperature of the moving object which is different from that of the background. Thus, the detection system has an electrical circuit operatively coupled to the heat sensor for producing a detection signal in response to the heat sensor detecting a change of temperature as, for example, caused by the body heat of a person entering the detection pattern.
The sensitive area of the heat sensor is too small to detect a significant amount of heat energy radiated from a human body by using the heat sensor alone. Thus, the detection system typically employs a lens made up of an array of Fresnel lens segments in a configuration for collecting and focusing a significantly greater amount of heat energy on the heat sensor than would be received using the heat sensor alone. A Fresnel lens segment is most efficient when it is flat. However, typically a lens array of Fresnel lens segments must be provided in a curved configuration in order to collect and focus the desired amount of heat energy on the heat sensor from a wide angle detection pattern. Thus, the lens array of Fresnel lens segments approximate this flatness by being provided as close-to-flat vertical segments arranged in a contiguous side-by-side relationship along a curve of constant radius.
One particular motion detection system is a low profile wide field of view optical system that employs an optical window in front of the Fresnel optical lens. The optical window has a relatively large flat main portion with opposite curved end portions. The Fresnel optical lens has the aforementioned curved configuration. A need exists for a structure to mount and enclose both the optical window lens and Fresnel optical lens in the desired arrangement.